The invention provides an injection molding method comprising supplying a gas into a molten resin in a plasticizing cylinder and injecting the molten resin having the gas dissolved therein, wherein when the resin is being plasticized, a gas space with a predetermined gas pressure is formed within th
The invention provides an injection molding method comprising supplying a gas into a molten resin in a plasticizing cylinder and injecting the molten resin having the gas dissolved therein, wherein when the resin is being plasticized, a gas space with a predetermined gas pressure is formed within the plasticizing cylinder in a gas supply section and the pressure at the front end of the screw is adjusted to be at least equal to the gas pressure in the gas space and within a range where the gas space can be maintained within the plasticizing cylinder in the gas supply section. According to the invention, the necessary amount of gas can be dissolved in the molten resin with good reproducibility in a quantitative manner.
대표청구항▼
1. An injection molding method comprising supplying a gas into a molten resin in a plasticizing cylinder and injecting the molten resin having the gas dissolved therein, wherein when the resin is being plasticized, a gas space with a predetermined gas pressure is formed within the plasticizing cylin
1. An injection molding method comprising supplying a gas into a molten resin in a plasticizing cylinder and injecting the molten resin having the gas dissolved therein, wherein when the resin is being plasticized, a gas space with a predetermined gas pressure is formed within the plasticizing cylinder in a gas supply section and the pressure at the front end of a screw is adjusted to be at least equal to the gas pressure in the gas space and within a range where the gas space can be maintained within the plasticizing cylinder in the gas supply section,wherein the plasticizing cylinder is equipped with a multi-stage type screw comprising a front end side screw stage having screw flights wherein notches are formed in at least one of said screw flights and the gas and the molten resin are kneaded to dissolve the gas into the molten resin while part of the molten resin is caused to flow backward by means of said notches, and wherein the gas pressure in the gas space is kept at a predetermined level to control the gas dissolution amount. 2. The injection molding method according to claim 1, wherein the gas pressure in the gas space formed in the gas supply section is detected and the pressure at the front end of the screw is controlled on the basis of this gas pressure.3. The injection molding method according to claim 1, wherein the molten resin is transferred in a starved state within the gas supply section.4. The injection molding method according to claim 1, wherein the pressure at the front end of the screw exerted during plasticization is also retained during the screw shutdown period from the end of plasticization to the start of injection.5. The injection molding method according to claim 1, wherein the gas is carbon dioxide.6. The injection molding method according to claim 1, wherein the plasticizing cylinder is equipped with a multi-stage type screw in which a stage comprising, in the following order from the resin supply section side toward the front end side of the screw, a feed section, a compression section and a metering section is repeated a plurality of times in series, and the gas supply section is located within the feed section of the front end side screw stage.7. The injection molding method according to claim 6, wherein a flow control section presenting high resistance to the flow of the molten resin is provided in the metering section of the rear end side screw stage of the plasticizing cylinder.8. The injection molding method according to claim 6, wherein the plasticizing cylinder is equipped with a mechanism for preventing a back-flow of the molten resin in the metering section of the rear end side screw stage.9. The injection molding method according to claim 1, wherein the gas supply into the plasticizing cylinder in the gas supply section is effected via an automatic on-off valve which is pressed by a spring onto a valve seat provided on the perimeter of an opening in a gas supply channel that extends into the plasticizing cylinder and which, when gas is supplied into the gas supply channel, is pushed against the spring by the pressure difference between the supply pressure and the pressure within the cylinder in the gas supply section and moved into the plasticizing cylinder to open the gas supply channel.10. An injection molding apparatus which comprises a plasticizing cylinder and a gas supply device for supplying a gas into a molten resin in the plasticizing cylinder and which injects the molten resin having the gas dissolved therein,wherein said plasticizing cylinder has a multi-stage type screw in which a stage comprising, in the following order from the rear end side toward the front end side in the direction of injection, a feed section, a compression section and a metering section is repeated a plurality of times in series, and which is also equipped with a gas supply channel open to the feed section of the front end side screw stage, wherein said gas supply device is connected to the gas supply channel, and wherein notches are in at least one screw flight in the feed section of the front end side screw stage. 11. The injection molding apparatus according to claim 10, further comprising a pressure sensor for detecting the pressure of the gas supplied into the plasticizing cylinder via the gas supply channel and a control unit for controlling the pressure at the front end of the screw on the basis of the pressure as detected with said sensor.12. The injection molding apparatus according to claim 10, further comprising an automatic on-off valve, which is pressed by a spring onto a valve seat provided on the perimeter of an opening in the gas supply channel that extends into the plasticizing cylinder and which, when gas is supplied into the gas supply channel, is pushed against the spring by the pressure difference between the supply pressure and the pressure within the cylinder in the gas supply section and moved into the plasticizing cylinder to open the gas supply channel.13. The injection molding apparatus according to claim 10, wherein a flow control section presenting high resistance to the flow of the molten resin is provided in the metering section of the rear end side screw stage.14. The injection molding method according to claim 1, wherein the total area of the notches accounts for 1/50-½ of the total area of the screw flights, wherein the area of each notch and that of each screw flight are based on the area of projection in the direction of the central axis of the screw.15. The injection molding apparatus according to claim 10, wherein the total area of the notches accounts for 1/50-½ of the total area of the screw flights, wherein the area of each notch and that of each screw flight are based on the area of projection in the direction of the central axis of the screw.
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이 특허에 인용된 특허 (10)
Cheng Alan T. (Livingston NJ), Apparatus and method for producing and molding structural foam.
Ladney ; Jr. Michael (18125 E. Ten Mile Rd. East Detroit MI 48021), Method of manufacturing structural foam plastic products free from undesirable contaminant constituents.
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